An important component of goal-directed behavior is the ability to voluntarily attend to a specific location, even before objects appear at that location. Brain regions in the parietal and temporal lobes control the allocation of spatial attention by modulating activity in early sensory regions, including visual cortex. These control regions are damaged in disorders of spatial attention such as unilateral neglect, a common and devastating syndrome that afflicts many stroke victims. Fortunately, visual cortex is often spared direct damage in many patients with neglect, although activity in this region is abnormal due to lack of appropriate modulation by control regions. Restoration of control over visual cortex is a potential means of intervention in patients with neglect. The long-term objective of this research proposal, therefore, is to understand the changes that higher-level brain regions produce in visual cortex to produce the behavioral phenomenon of spatially directed attention. Because there are independent resources for attending to the left and right sides of space, it is important to understand the changes in visual cortex that allow for the specific allocation of attention across (specific aim 1) and within (specific aim 2) visual hemifields. Blood oxygen level dependent (BOLD) imaging in healthy human subjects will be used to meet these objectives. By measuring neural signals following auditory spatial cues and prior to visual stimulation, it is possible to examine endogenous control signals in visual cortex uncontaminated by visual stimulus-evoked activity. Measurement of the distribution of endogenous signals across visual cortex during explicit manipulation of the locus of spatial attention as well as the location of upcoming distracting visual objects will indicate how precisely visual cortex can be modulated. Furthermore, the relationship of endogenous control signals to accuracy on an upcoming perceptual task at the locus of spatial attention provides a strong indication of the modulations essential for optimal goal-directed behavior. Some of the dysfunction associated with unilateral neglect, a disorder of spatial attention, is due to the loss of normal control over structurally intact brain regions. The goal of this research is to understand how control is exerted over these regions in healthy individuals, with the long-term aim of restoring appropriate control in sufferers of neglect. In addition, understanding the neural mechanisms of spatial attention may inspire directed therapies in other disorders of attention, including traumatic brain injury, schizophrenia, and attention deficit hyperactivity disorder.